1. Field of the Invention
The present invention relates to a heat treatment apparatus and a method of heat treatment, more particularly relates to a heat treatment apparatus in the process of production of semiconductor chips or liquid crystal display (LCD).
2. Description of the Related Art
In the process of production of semiconductor chips, an LCD, etc., a wafer or substrate is given desired patterns by utilizing photolithography for removing unnecessary portions. In photolithography, the unnecessary portions other than the desired patterns are generally removed by etching using a chemical. On the other hand, the required portions are protected by a photoresist, so remain even after the etching and thereby can give the desired patterns. Photolithography is used for forming for example circuit patterns on a wafer for semiconductor chips and is used for forming indium-tin oxide (ITO) and other patterns on a substrate for an LCD.
An example of photolithography will be schematically explained below step by step. First, a coating solution containing photoresist film components is coated on for example a wafer by spin coating or another method. The wafer coated by the coating solution is heat treated as an object to be heat-treated whereby the solvent in the coating solution is evaporated away and a uniform photoresist film is formed. This heat treatment will be referred to as “pre-baking”. Then, the photoresist film is developed by being exposed by UV rays or the like using a mask having desired patterns formed therein. Then, for example, the exposed portions are dissolved away by a chemical. On the other hand, the unexposed portions are polymerized and are not dissolved or hard to be dissolved in the chemical, so remain. In this way, the resist patterns are developed. Then, the photoresist film forming the resist patterns is further heat treated in order to bond it with the wafer. This heat treatment will be referred to as “post-baking”. Next, this is etched to remove the unnecessary portions other than the portions protected by the resist patterns. Thereafter, the resist patterns are peeled away, whereby the desired patterns are formed on the wafer.
As explained above, in this series of photolithography steps, pre-baking, post-baking, and other heat treatment are carried out by using a heat treatment apparatus. FIG. 6 is a schematic vertical sectional view of a heat treatment apparatus. The heat treatment apparatus is provided with a stage 1 for placing a wafer W or other heated object on which the coating solution is coated and a heating unit 2 for heating the object to be heat-treated and the coating solution. The space above this stage 1 is covered by a cover portion 3 having a body 3a and a top plate 3b. The cover portion 3 is formed with an exhaust port 4 for exhausting the solvent and other volatile components generated from the heated object by the heat treatment to the outside of the heat treatment apparatus. This exhaust port 4 is connected to an exhaust duct of an exhaust treatment system etc. for treating the volatile components.
When using a heat treatment apparatus for heat treatment, the following disadvantages exist. When placing a wafer W on which the coating solution containing the photoresist film components is coated is placed on the stage 1 and heated by a heater 2a of the heating unit 2, the solvent component in the coating solution is volatilized due to the heating. This coating solution includes sublimating components such as low molecular-weight components of the photoresist film material. For this reason, also the sublimating components subliminate along with the volatilization of the solvent component. Then, the gaseous mixture of this sublimating components and the volatilizing components is exhausted to the outside of the heat treatment apparatus from the exhaust port 4. When it is sent to the exhaust port 4, the sublimating components sometimes stick to the top plate 3b or the like and become solids. Then, the solids sticking to the top plate 3b or the like sometime drop down to the wafer W or the stage 1 to be heat treated and cause defects in pattern formation etc. For this reason, they sometimes becomes a cause of a drop in the yield of the semiconductor chips (or LCD) or a drop in the reliability. Further, when gas containing the sublimating components is exhausted from the exhaust port 4, in the same way, since the gas is cooled inside the exhaust duct, the exhaust treatment apparatus, etc., it sometimes becomes a solid. As a result, the exhaust duct and the exhaust treatment apparatus become fouled, and the exhaust treatment efficiency was sometimes lowered.
In order to avoid the present disadvantage, the heat treatment apparatus has been periodically subjected to a maintenance routine or a material producing little sublimating components has been selected in the design of the photoresist film to be used. In the former periodic maintenance, for example, the work of replacing or washing the top plate 3b and other parts of the cover portion 3 or washing the exhaust duct and the exhaust treatment apparatus has been performed. However, this work is troublesome, so is not easy, and further the heat treatment apparatus had to be stopped during the work, so the production efficiency was sometimes lowered. Further, in the latter material design of the photoresist film, while reduction of the sublimating components was possible, it was difficult to completely eliminate them. In this way, periodic maintenance was indispensable, so a drop in the production efficiency occurred.
Various inventions have been proposed with respect to these disadvantages (for example, Japanese Unexamined Patent Publication (Kokai) No. 2000-173883), but none were sufficient.
Summarizing the disadvantage to be solved by the invention, as explained above, in the above heat treatment apparatus, sometimes the sublimating substances generated by the heat treatment became solids and dropped down causing poor quality and a decline in the yield of the product. For example, in the photolithography of semiconductor chips or LCDs, when the wafer or substrate on which the coating solution containing the photoresist film components was coated was heat treated, after the sublimating components produced due to the heat treatment became solids, the solids sometimes dropped down to the wafer causing defects in pattern formation. Further, a drop in the yield of the semiconductor chips or LCDs and a decline in the reliability sometimes occurred. To prevent the sublimating components from falling to the wafer or substrate, periodic maintenance of the heat treatment apparatus became necessary resulting in a drop in the production efficiency.